343 already "tried something fresh" with Halo 4 when they modernized the franchise with perks, loadouts, and all that other nonsense.
You can introduce new and interesting mechanics that build on Halo's strengths without ruining the things people like about the gameplay. It's not easy, but it's possible. The problem is that the designers need to be both knowledgeable enough about Halo, and creative enough to come up with ideas that are fresh and interesting. I always say things like vehicle-boarding and theater mode are fantastic additions to Halo that only improved the franchise. Maybe more unique and interesting gametypes, map designs, and weapons could be enough to "refresh Halo" -- they're certainly things I'd like to see. Not weapon customization, not Titanfall-esque movement, not vehicle ordnance. The point is, there are smarter ways to go about doing this rather than copying the more popular games out there or compromising and segmenting your playerbase to try to appease everyone.
Besides, where do asymmetric objective maps like Terminal and Zanzibar fit into this split-multiplayer experience? Those were built for 4v4 to 6v6, but vehicles were an integral part of them. 1 Flag and Assault on those maps were super competitive, teamwork-oriented, and god damn amazing. You're not going to have anything close to a similar experience when there are 32 players with random abilities running around with eight scopes and three grenade launchers on their DMRs. If you have to have player ability, weapon, and vehicle customization, put it in Firefight -- it's unlikely to hurt anyone there.